Segment shift arrangement

ABSTRACT

A plurality of type bars are pivotally supported in a type bar segment and urged to a rest position by a plurality of springs acting on sublevers linked to the type bars. The type bar segment is supported by a bail and movable in an arc between a lowered position and a raised position to provide an over-center motion enabling the sublever return springs to maintain the segment at either position. The upper and lower positions of the type bar segment are determined by a member which is associated with the segment and slidable on a post having stops threaded thereon for easy adjustment. The type bar segment is driven between the raised and lowered positions by an eccentric cam coupled through a spring clutch normally constricting about a hub of a rotatably driven power roll, and the spring clutch is selectively disengaged when the type bar segment is at the raised and lowered positions by corresponding stop abutments which engage a free end of the spring so as to prevent engagement with the power roll. The type bars are driven in a printing movement by cams carried on the sublevers and engaging the rotating power roll, and the impact intensity of the type bars is controlled by a stop member limiting the engagement of the cams with the power roll. To compensate for differences in the printing area of the type characters on each type bar, the position of the stop member is varied with the shifting of the type bar segment.

United States Patent [191 Madison SEGMENT SHIFT ARRANGEMENT [75] Inventor: Theodore N. Madison, Rocky Hill,

Conn.

[73] Assignee: Litton Business Systems, Inc., New

York, N.Y.

221 Filed: Feb. 28, 1973.

211 App1.No.:336,775

[52] US. Cl. 197/74, 197/17 [51] Int. Cl B41j 7/50 [58] Field of Search 197/17, 33, 41, 71, 72, 197/74, 75, 76, 77, 81

[56] References Cited UNITED STATES PATENTS 1,945,097 1/1934 Thompson et a1. 197/41 X 2,275,759 3/1942 l-lelmond 197/74 2,681,129 6/1954 Yaeger 197/74 X 2,818,152 12/1957 Letterman 197/17 2,868,345 l/1959 Nitschke 197/17 2,900,062 8/1959 Nitschke 197/17 3,077,255 2/1963 Coleman et al.. 197/17 3,179,226 4/1965 Bolton 197/17 3,228,511 1/1966 Meinherz 197/41 X 3,250,365 5/1966 Klingner et a1.. 197/17 3,250,366 5/1966 Rix et a1. 197/17 3,393,786 7/1968 Heidt 197/17 3,393,787 7/1968 Dodge et a1. 197/74 X 3,536,172 10/1970 Frechette..... 197/17 UX 3,568,811 3/1971 Johnson 197/71 X 3,623,587 11/1971 Link 197/17 1 Jan. 14, 1975 Primary Examiner-Ernest T. Wright, Jr. Attorney, Agent, or Firm-Joseph R. Spalla [57] ABSTRACT A plurality of type bars are pivotally supported in a type bar segment and urged to a rest position by a plurality of springs acting on sublevers linked to the type bars. The type bar segment is supported by a bail and movable in an are between a lowered position and a raised position to provide an over-center motion enabling the sublever return springs to maintain the segment at either position. The upper and lower positions of the type bar segment are determined by a member which is associated with the segment and slidable on a post having stops threaded thereon for easy adjustment. The type bar segment is driven between the raised and lowered positions by an eccentric cam coupled through a spring clutch normally constricting about a hub of a rotatably driven power roll, and the spring clutch is selectively disengaged when the type bar segment is at the raised and lowered positions by corresponding stop abutments which engage a free end .of the spring so as to prevent engagement with the power roll. The type bars are driven in a printing movement by cams carried on the sublevers and engaging the rotating power roll, and the impact intensity of the type bars is controlled by a stop member limiting the engagement of the cams with the power roll. To compensate for differences in the printing area of the type characters on each type bar, the position of the stop member is varied with the shifting of the type bar segment.

3 Claims, 10 Drawing Figures PATENTED 1 75 sum 2 or 6 mm l SHEET 3 0F 6 PATENTEB JAN 1 4|975 PATENTED JAN] 4|97S SHEET UF 6 Y PATENTEU JAN 1 4 5 SHEET 5 0F 6 SEGMENT SHIFT ARRANGEMENT This invention relates to a power driven typewriter, and more particularly to a segment shift arrangement.

In a power driven typewriter, a plurality of type bars are pivotally supported in a type bar segment and urged to a rest position by springs acting on a plurality of type bar linkages each connected to a different type bar. Each of the type bars carries a pair of type characters typically having different printing areas, and each type bar linkage carries a cam for engagement with a rotatably driven power roll. Printing of a selected character is effected by moving the corresponding cam into engagement with the power roll to drive the type bar from the rest position to a printing position to impact one of the type characters against a recording medium. The type characters are spaced apart along the type bar, and selected printing with one or the other type character is achieved by shifting the type bar segment between a lowered and a raised position to enable one or the other type character to impact against the platen.

To obtain satisfactory printing with either of the type characters carried on each of the type bars, it is necessary that the type bar segment be evenly aligned parallel with the platen in both raised or lowered positions, and that the raised and lowered positions of the type bar segment be accurately adjusted so that each type character will impact fully against the platen. Moreover, to prevent blurring, the type bar segment must be stationary at the momment a type character impacts against the platen. To compensate for the difference in the printing areas of the type characters carried on each type bar, the impact intensity of the type bars must be varied in accordance with the shifting of the type bar segment to the raised or lowered positions.

An object of the present invention is to provide a segment shift arrangement which minimizes the number of parts and enables only the springs acting on the type bar linkages to hold the segment at either the raised or lowered positions.

Another object of the invention is to'provide a segment shift arrangement which varies the impact intensity of the type characters according to the shifted position of the type bar segment and enables the range of impact intensity between the two positions to be varied in accordance with a particular type style.

Still other objects, features, and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailled description of the present invention, taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a partial diagrammatic view of a powered type action and segment shift arrangement constructed in accordance with the present invention;

FIG. 2 is another view of the arrangement shown in FIG. 1 and illustrating the shifted positions of the segment shift arrangement;

FIG. 3 is a rear perspective view illustrating the suspension of the segment shift arrangement and a drive arrangement for shifting the type bar segment between the raised and lowered positions;

FIG. 4 is a side view of the drive arrangement shown in FIG. 3;

FIG. 5 is a partial cross-sectional view of the drive arrangement shown in FIG. 3;

FIG. 6 is a partial view of a shift mechanism shown in FIG. 4 and illustrating the type bar segment in a lowered position;

FIG. 7 shows an impression control mechanism for varying the impact intensity of the type bars;

FIG. 8 is a partial cross-sectional view of the impression control mechanism shown in FIG. 7 and illustrating the condition of the arrangement to minimize the impact intensity of the type bars;

FIG. 9 is a view similar to FIG. 8 and illustrating the condition of the arrangement to maximize the impact intensity of the type bars; and

FIG. 10 shows the mechanism for varying the impact intensity with the shifting of the type bar segment to compensate for the different printing areas of the type characters carried on each type bar.

Referring now in detail to the figures in the drawing and more particularly to FIG. 1, there is shown one of a plurality of powered type actions in a type action arrangement, generally indicated at 11, for impacting against a platen 13. The type characters 15, or other symbols to be printed are formed on a type head 17 which is carried on the end of a type bar 19, and the type bar 19 is supported for a printing movement from a rest position ro rhw platen 13. As is conventional, printing is effected by impacting one of the type characters 15 against the recording medium, and the type bar 19 is driven in a printing movement by depressing a type key 21 forming a portion of a keyboard to cause a key actuating means, generally indicated 23, to move a cam 25 into engagement with a power roll 27 which may be rotatably driven by a suitable motor, not shown. The cam 25 is pivotally supported on a type bar linkage, generally indicated 29, and drives the type bar 19 to the printing position as the cam 25 moves in engagement with the rotating power roll 27. The recording medium and the motor for driving the'power roll 27 are not shown since they form no part of the present invention and may be desirably conventional. Furthermore, other portions of the typewriter are shown in other copending U.S. applications. For example, the drive for the power roll 27 is illustrated and described in a copending application Ser. No. 333,389 filed Feb. 16, 1973 of Theodore N. Madison and entitled Typewriter Carriage Jam Precluding and Action Jam Release Mechanism and the detailed construction of the type action arrangement is disclosed in a copending application Ser. No. 333,295 filed Feb. 16, 1973 of Theodore N. Madison and entitled Type Action Arrangement.

As shown, the type bar 19 is guided for movement in a slot 31 formed in a type bar segment 33 and pivotally supported about a pivot wire 35 received through an opening 36 formed in a type bar segment 33, as is conventional. The type bar 19 is driven by the cam 25 through the type bar linkage 29 which includes a sublever 37 which is pivotally supported and connected to the type bar 19 by a link 39. The type key 21 for operating the key actuating means 23 is carried on a keylever 41 which is pivotally supported and has a projecting finger 43 for rocking an L-shaped trip lever 45 which is also pivotally supported. The L-shaped trip lever 45 has one arm 47 which is contacted by the finger 43 while the end of the other arm 49 contacts a shoulder 51 of the pivotally supported cam 25 for moving it into engagement with the power roll 27. In the rest position, the type bar 19 is normally urged against a headrest 53 by a resilient biasing means in the form of a sublever return spring 55, and the type key 21 is normally urged to a rest position by a resilient biasing means in the form of another spring 57. To insure that the type key 21 undergoes the same distance of depression each time the type action 11 is operated, the cam 25 has a rearward portion 59 which is urged against a stop 61 formed on the end of the sublever 37 by a further resilient biasing means in the form of a spring 63 which is stretched between the cam 25 and a suitable projecting portion 65 of the sublever 37.

When the type key 21 is depressed to initiate the operation of the type action 1 l, the keylever 41 is pivoted downwardly so as to pivot the trip lever 45 clockwise and move the cam 25 into engagement with the rotatably driven power roll 27. As the cam 25 is driven by frictional engagement with power roll 27, the sublever 37 is pivoted rearwardly away from the power roll 27 and against the urging of the spring 55 so as to drive the type bar 19 from the rest position and toward the printing position at the platen 13. The driving movement of the cam 25 continues until the rearward end 59 of the cam 25 engages a stop member 67, and subsequently the cam 25 returns to the stop 61 of the sublever 37 under the urging of the spring 63 whie the momentum of the type bar 19 continues to move it toward the platen 13 against the urging of the sublever return spring 55. After the type character impacts against the platen 13, the type bar 19 is returned to the headrest 53 under the urging of the sublever return spring 55 while the trip lever 45 and the keylever 41 are returned to the rest position under the urging of the spring 57.

As is conventional, the type characters 15 formed on the type head 17 are spaced apart from each other along the type bar 19 with one type character 15', usually a lower case type character such as r, being closer to the pivot wire 35 while the other type character 15", usually an upper case type character such as R, being further from the pivot wire 35. Typically, the type bar segment 33 is maintained at a raised position, generally indicated at 69' in FIG. 2, to print the type character 15' and selective printing of the other type character 15' is achieved by depressing a shift key 71 forming a portion of the keyboard to cause a shift actuating means, generally indicated 73, to operate a shift drive, generally indicated 75, to move the type bar segment 33 to a lowered position, generally indicated 69' in FIG. 2. Subsequently, the type bar segment 33 may be returned to the raised position 69' by releasing the shift key 71. As shown, the shift key 71 is carried on a keylever 79 which is pivotally supported and has a projecting finger 81 for pivoting a shift actuating member 83 which is normally urged to a rest position by a resilient biasing means in the form of a spring 85 stretched between the shift actuating member 83 and a suitable portion of the typewriter frame. Since the shift actuating means 73 is similar to the key actuating means 23, and is supported in a similar manner, no further detailed descritpion is believed necessary.

To print a series of type characters 15 evenly along a line of type, the type bar segment 33 must be correctly positioned relative to the platen 13, both vertically and horizontally, so that each type character 15 fully impacts against the platen 13 with the same alignment, and this alignment must be maintained when the type bar segment 33 is shifted to either the raised or lowered position 69', 69". Moreover, the shifting of the type bar segment 33 must not change the normal rest position of the sublevers 37 since that would change the distance of keylever depression necessary to pivot the cams 25 into engagement with the power roll 27 and alter the engagement of the cams 25 with the power roll 27. Furthermore, the shifting of the type bar segment 33 must be achieved with a minimum of bouncing which may cause blurring of the print work if a type character 15 impacts the platen 13 while the type bar segment 33 is still in motion.

ln the past, the type bar segments 33 have often been supported in ball races and movable in a straight path requiring latches or other means to hold them at the shifted positions 69', 69" respectively. Alternatively, the type bar segment 33 has been supported in a manner requiring additional springs or symmetrical shift drive arrangements to support the type bar segments 33 at the shifted positions 69', 69". Moreover, to avoid bouncing of the type bar segment 33 upon shifting to either the raised or lowered positions 69', 69" respectively, typewriters have sometimes been provided with dashpots to dampen excessive movement. Furthermore, it has often been necessary to provide set screw adjustments to evenly position the type bar segment 33 relative to the platen 13. However, the use of ball races, latches, dashpots and symmetrical shift drives to obtain satisfactory shifting of the type bar segment 33 undesirably increases the complexity of the typewriter and the cost and difficulty of constructing it.

In accordance with the present invention, the type bar segment 33 is movable in an are upon shifting between the raised and lowered positions 69', 69" respectively so as to provide an over center movement enabling only the sublever return springs 55 to urge the type bar segment 33 to the shifted positions 69', 69" respectively and hold it there. Adjustable limit means are provided to correctly determine the raised and lowered positions 69, 69" respectively of the type bar segment 33 relative to the platen 13, and the shift drive 75 is arranged to decelerate the type bar segment 33 as it is driven to either the raised or lowered positions 69', 69" by the shift drive 75 and under the urging of the sublever springs 55.

As more particularly shown in FIGS. 2 and 3, the type bar segment 33 is attached to a suitable bracket 87 which is pivotally supported for movement in an are by a bail, generally indicated 89. The bail 89 is in the form of a pair of arms 89', 89" fixedly secured to a shaft 91 which is rotably supported between a pair of side walls 93', 93" serving as a portion of the typewriter frame. Since the type bar segment 33 is carried on a single supporting member 87, the type bar segment 33 is easily alignable with the platen 13 by inserting the shaft 91 through suitable openings in the side walls 93', 93". To adjust the raised and lowered positions 69', 69" of the type bar segment 33 for properly impacting the type characters 15', 15", the bracket 87 has a positioning member 99 extending rearwardly from the type bar segment 33 with an opening 101 for receiving therethrough a guide member 103 having a pair of nuts 105', 105" suitably threaded thereon. The guide member 103 may be secured to the frame of the typewriter by suitable means and the nuts 105', 105" may be threadably adjusted to correctly determine the raised and lowered positions 69', 69" respectively of the type bar segment 33.

To shift the type bar segment 33 between the raised and lowered positions 69', 69" respectively, and decelerate the segment 33 as it approaches either positions 69', 69" so as to avoid bouncing, the shift drive 75 is in the form of an eccentric cam 107 rotatably supported about the axis of the power roll 27 and selectively coupled thereto by a spring clutch 109. As more particularly shown in FIGS. 3-6, the eccentric cam 107 is rotatably supported about a hub portion 111 of the rotatable power roll 27 with the eccentric camming surface disposed in a circular opening 113 formed in a shift link 115 which is pivotally connected to a crank 117 secured to the end of the bail 89. The spring 109 is coiled about the same hub portion 111 of the rotatable power roll 27 with one end 118 suitably connected to the eccentric cam 107 and the other end 119 extending freely and radially from the hub 111. The spring clutch 109 normally constricts about the hub portion 111 to couple the eccentric earn 107 to the rotatable power roll 27, but the spring clutch 109 may be enlarged to prevent coupling upon engagement of the free end 119 with either of two stop abutments 121', 121" formed on the shift actuating member 83.

As previously described, the shift actuating member 83 is normally biased by the spring 85 to maintain the type bar segment 33 in the raised position 69 for typing the lower case type character In this position, the stop abutment 121 is in blocking engagement with the free end 119 of the spring clutch 109 so as to enlarge the spring clutch 109 and prevent shifting. When the shift key 71 is depressed to shift the type bar segment 33 to the lowered position 69 for printing the upper case type characters 15", the shift actuating member 83 is pivoted against the urging of the spring 85 to remove the stop abutment 121' from blocking engagement with the free end 119 and enable the spring clutch 109 to grip the hub 111 of the power roll 27 and rotatably drive the eccentric cam 107. The rotation of the eccentric cam 107 pulls the shift linkage 115 downwardly to move the type bar segment 33 from the raised position 69, and along an arcing path, thereby pivoting the sublevers 37 against the urging of the return springs 55. Upon approaching the lowered position 69", the movement of the type bar segment 33 is slowed by the action of the eccentric cam 107 while the return springs 55 urge it to the selected position 69". Finally, as shown in FIG. 6, the free end 119 of the clutch spring 109 engages the stop abutment 121" of the pivoted shift actuating member 83, thereby disengaging the shift drive 75. Subsequently, the type bar segment 33 may be returned to the raised position 69 by releasing the shift key 71 to enable the shift actuating member 83 to return to its normal position under the urging of the spring 85 so as to remove the stop abutment 121" from blocking engagement with the free end 119 of the spring clutch 109 to actuate the shift drive 75 until the free end 119 engages the stop abutment 121' as shown in FIGS. 3 and 4.

Since the pair of type characters 15',l5" usually have significant differences in printing areas, with one of the type characters 15' being a lower case letter, for example r, and the other type character 15" being an upper case letter, for example r, and the other type character 15" being an upper case letter, for example R, it is desirable to vary the impact intensity of the type bars 19 with the shifting of the type bar segment 33 so as to achieve the uniform printing along a line of type. As previously described, the type bars 19 are driven in a printing movement by the engagement of the earns 25 with the power roll 27, and the impact intensity may be varied by controlling the engagement of the earns 25 with the power roll 27. As more particularly shown in FIGS. 7-9, the stop member 67 limiting the engagement of the cams 25' with the rotatable power roll 27 is part of an impression control mechanism, generally indicated 123, for uniformly varying the impact intensity of all of the type bars 19. As shown, the stop member 67 is in the form of a bail pivotally supported between the side plates 93', 93" and movable between a position enabling maximum engagement of the earns 25 with the power roll 27, as shown in FIG. 9, and a position providing minimum engagement of the earns 25 with the power roll 27, as shown in FIG. 8. The stop member 67 is normally urged to the position of FIG. 9 by a spring 125 stretched between a suitable portion of the side plate 93' and a projection 127 of the impression control stop member 67 which extends through an opening 129 in the side plate 93', and the stop member 67 may be moved between the two positions by the operation ofa control member 131 located at the keyboard. As more particularly described in the previously identified copending US. application entitled Type Action Arrangement, the control member 131 is connected in controlling relation with the impression control stop member 67 by a link 133 which extends beneath a stub shaft 135 and has a camming surface 137 engaging the projection 127 for selectively adjusting the position of the stop member 67.

To vary the engagement of the cams 25 with the rotatable power roll 27 in accordance with the shifting of the type bar segment 33, the segment shift arrangement of the present invention is provided with a camming means for operating on the linkage 133 so as to change the position of the impression control stop member 67 when the type bar segment 33 is shifted. As more particularly shown in FIG. 10, the camming means, generally indicated 139, includes a camming member 141 pivotally supported on the stub shaft 135 and having a camming surface 142 engaging a flange 145 formed on the linkage 133. The camming member 141 is pivoted in accordance with the shifting of the type bar segment 33 by a connecting link 147 which is pivotally connected to a crank 149 suitably secured to the end of the shaft 91. Accordingly, the shifting of the type bar segment 33 between the raised and lowered positions 69, 69" respectively, pivots the camming member 141 to move the impression control stop member 67 in a direction enabling greater engagement between the cam 25 and the power roll 27 so as to increase the impact intensity of the type character 15' against the platen 13. Likewise, the shifting of .the type bar segment 33 to the raised position 69 enables the urging of the spring 125 to move the stop member 67 in a direction reducing the engagement of the cam 25 with the power roll 27.

Since the difference in printing areas of the type characters 15' and 15" may vary according to different type styles, it is desirable to provide means for adjusting the variation in impact intensity of the type characters accompanying a shifting of the type bar segment 33. As more particularly shown in FIGS. 7 and 10, the connecting link 147 is connected to the crank 149 by a suitable nut and bolt arrangement, generally indicated 151, which is received in a slot 153 formed in the crank 149. Accordingly, by adjusting the connecting link 147 to different positions along the slot 153 formedin the crank 149, the pivoting of the camming member 141 may be adjusted to provide a variation in the impact intensity generally matching the difference in the printing areas of the type characters 15" for a particular style of type.

What is claimed is: 1. Case shift mechanism for a typewriter comprising a frame,

a plurality of type bars each of which has upper and lower case type characters thereon, a type bar segment pivotally supporting said plurality of type bars, a power roll, a plurality of sublevers pivotally mounted on said frame, links connecting an associated sublever to an associated type bar, each of said sublevers rotatably mounting a cam operative when engaged with said power roll to drive its associated sublever and connected type bar I from a rest position, means defining segment upper case and lower case limit positions, means for moving said segment from the case limit position toward the other case limit position along an are including a shaft pivotally mounted on said frame, a pair of arms secured to said shaft and pivotally connected at the ends thereof to said segment, and means for rocking said shaft to move said segment,

said pivotal connection of said arms and segment being movable to said limit positions through a line through the center of said shaft and parallel to said links connecting sublevers and type bars, and

a plurality of type bar return springs connected to each of said sublevers acting collectively as the sole agency to urge said pivotal connection toward a limit position after it has been moved through said line incident to movement of said segment thereby to detentably hold said segment in one or the other case limit position.

2. Mechanism as recited in claim 1, said means defining segment upper case and lower case positions comprising a segment extension having an opening formed therein,

a guide member mounted on said frame and extending through said opening in said segment extension, and means on said guide member defining the upper and lower limits of movement of said extension.

3. Mechanism as recited in claim 1, said means for rocking said shaft comprising a crank arm secured to said shaft,

power operated means including an eccentric cam, a

half revolution clutch connected between said power roll and said eccentric cam, a cam follower linked to said crank arm, and means to operate said clutch to effect a case shift operation.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,860.403 Dated J r 14. 1975 Inventor(s) Thegdore N Madj son It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In The Specification:

Column 1, line 50, change "detailled" to --detailed--.

Column 2, line 25, change "ro" to --to--; same line, change "rhw" to --the--.

Column 3, line 24, change "whie" to --while--.

line 43, change "15"" to --l5"--.

line 47, change "69'" to --69"--.

line 59, change "descritpion" to --description--.

Column 5, line 13, after "spring" insert --clutch--.

lines 62-63, cancel "and the other type character 15'' being an upper case letter, for example "r",".

Column 6, line 26, after "plication" insert --Serial No. 333,295".

line 54, change "15'" to -l5"--.

In The Claims:

Column 7, Claim 1, line 27, change "the" to --one--.

Signed and sealed this 5th day of April 1975.

(SEAL) Attst C. I=TARSHALL DAM RUTH C. 1 .5 N Commissioner of Patents Attesting Officer and Trademarks (10-59) uscoMM-oc 60876-P69 k ".5. GOVIIIIIIIIT PRINTING OFFICE ID. O-QlG-SM, 

1. Case shift mechanism for a typewriter comprising a frame, a plurality of type bars each of which has upper and lower case type characters thereon, a type bar segment pivotally supporting said plurality of type bars, a power roll, a plurality of sublevers pivotally mounted on said frame, links connecting an associated sublever to an associated type bar, each of said sublevers rotatably mounting a cam operative when engaged with said power roll to drive its associated sublever and connected type bar from a rest position, means defining segment upper case and lower case limit positions, means for moving said segment from the case limit position toward the other case limit position along an arc including a shaft pivotally mounted on said frame, a pair of arms secured to said shaft and pivotally connected at the ends thereof to said segment, and means for rocking said shaft to move said segment, said pivotal connection of said arms and segment being movable to said limit positions through a line through the center of said shaft and parallel to said links connecting sublevers and type bars, and a plurality of type bar return springs connected to each of said sublevers acting collectively as the sole agency to urge said pivotal connection toward a limit position after it has been moved through said line incident to movement of said segment thereby to detentably hold said segment in one or the other case limit position.
 2. Mechanism as recited in claim 1, said means defining segment upper case and lower case positions comprising a segment extension having an opening formed therein, a guide member mounted on said frame and extending through said opening in said segment extension, and means on said guide member defining the upper and lower limits of movement of said extension.
 3. Mechanism as recited in claim 1, said means for rocking said shaft comprising a crank arm secured to said shaft, power operated means including an eccentric cam, a half revolution clutch connected between said power roll and said eccentric cam, a cam follower linked to said crank arm, and means to operate said clutch to effect a case shift operation. 